Diving beetles, rarity and responses to climate change

Research in ecophysiology and development

We use aquatic insects,
particularly water beetles, to explore a range of fundamental and applied
topics in ecology and evolution. Recent
studies have explored the biology of rarity, underwater gas exchange, and the
evolution of salinity tolerance, often within the context of global change.

Water beetles and rarity

Most species on earth are rare, sometimes being restricted to very small areas of the world, and often occurring in very low numbers. This is well known. What is not so well known is why most species are rare.

Work led by Prof David Bilton at University of Plymouth, is helping to provide some answers to this question, and also helping us to understand how rare and common species may respond to future climate change.

There are three main ideas as to why related species show dramatically different range sizes; these relate to evolutionary age (i.e. how long a species has had to spread), dispersal limitation (i.e. how good a species is at moving to new places) and fundamental niche breadth (i.e. the range of environmental conditions a species can tolerate).

Work at University of Plymouth has evaluated the relative importance of these three factors amongst closely related rare and common species, and demonstrated that there is often a fundamental link between niche breadth, in the form of ecophysiology (temperature tolerance, immune responses and metabolic plasticity) and range size.

Put simply, how common or rare a species is can often be accurately predicted from its physiological abilities. Species with narrower temperature tolerances, for example, are far more restricted, and it is these species which seem likely to be the most vulnerable to on-going climatic changes.

We have studied a number of clades of closely related species of European water beetles which vary dramatically in their geographical range size, from species restricted to areas in southern Europe to those which are found from the Mediterranean to northern Sweden.

The ability to tolerate temperature extremes was a very good predictor of the geographical range size of species, far more so than how good these species are at flying from place to place, or how long ago they evolved.

As with much of the biota of Europe, these beetles survived ice ages in southern Europe, moving north as the climate warmed 12,000 years ago. Present-day widespread species are those which have been able to retain their southern range boundaries, and expand north, something which requires relatively high tolerance to both heat and cold.

Species with narrower temperature tolerances are far more restricted, and it is these species which seem likely to be the most vulnerable to ongoing climatic changes. As well as having limited temperature tolerance, these rare species also have limited ability to adjust their tolerance windows as temperatures change.

Given that climate warming will also lead to a reduction in the availability of suitable aquatic habitats in Mediterranean areas, such restricted species would appear to be doubly threatened in the future.

Verberk, W.C.E.P. & Bilton, D.T. in 2015. Oxygen limited thermal tolerance is seen in a plastron breathing insect, and can be induced in a bimodal gas exchanger. Journal of Experimental Biology218: 2083-2088.